Plants require a variety of elements for adequate nutrition. The essential elements carbon, hydrogen, and oxygen are provided by carbon dioxide and water, materials which are usually available in adequate amounts from both the soil and the atmosphere. The supply of carbon dioxide and water is continually replenished by natural phenomena.
Thirteen other elements are known to also be essential to plant nutrition. These elements are normally drawn from the soil. If the soil nutrient supply is deficient, the application of fertilizer is necessary. Of these thirteen elements, nitrogen, phosphorus, and potassium are needed by plants in relatively large quantities and are accordingly called the macronutrients. Calcium, magnesium, and sulfur are generally required in lesser, though still substantial, amounts and are classified as secondary nutrients. The remaining seven elements are known as micronutrients since they are required in very small amounts for plants growth. These seven are iron, manganese, copper, zinc, molybdenum, chlorine, and boron.
The element boron functions as a regulator in the plant metabolism of carbohydrates. A boron deficiency causes a degeneration of meristematic tissue associated with a restriction in terminal growth; thickened, wilted or curled leaves; thickened, cracked or water-soaked petioles and stems; and discolored, cracked or rotted fruit, tubers, and roots. While a boron deficiency is obviously deleterious, an excess can also be harmful. Plants vary in their responses to both shortages and excesses of boron.
There are, of course, hundreds of known boron compounds, but most cannot be used by the plant as a source of elemental boron since, to serve as a boron source, the compound must supply the boron in a form which is both water-soluble and capable of passing through plant membranes. Sodium tetraborate, Na.sub.2 B.sub.4 O.sub.7.10 H.sub.2 O, is one boron compound which is known to supply elemental boron to plants. It is also the most widely used boron fertilizer. Sodium tetraborate, commonly known as either borax or sodium borate, is a dry solid and contains about 11 weight percent boron. Sodium tetraborate can be applied to the soil in several ways, all of which present difficulties.
First of all, sodium tetraborate can be applied by itself as a dust to the soil or foliarly to the plants. However, the recommended treatment is usually only a few pounds per acre and it is very difficult to evenly distribute such a small amount over an acre. Therefore, when sodium tetraborate is used in dry form, it is generally mixed with other solid fertilizers. But problems of uniform incorporation and segregation after mixing still exist.
For the above reasons, it is often more convenient to handle sodium tetraborate in liquid solutions. Unfortunately, the solubility of sodium tetraborate in water is relatively low. Furthermore, its use is limited with the many standard liquid fertilizer solutions providing nitrogen in the ammonium form because of the formation of the relatively insoluble ammonium borates. Such standard liquid fertilizers include the "NPK solutions," which provide nitrogen, phosphorus, and potassium in varying proportions, and the ammoniated chelated micronutrient solutions, which are sources of iron, manganese, copper, and zinc.
To meet the need for a boron fertilizer which is more soluble in water and in NPK solutions, the United States Borax & Chemical Corporation sells a product called SOLUBOR.RTM.. SOLUBOR.RTM. is a partially dehydrated combination of sodium tetraborate and sodium pentaborate, Na.sub.2 B.sub.10 O.sub.16.10 H.sub.2 O. It contains about 21 weight percent boron. Although it sells at a premium over sodium tetraborate, SOLUBOR.RTM. is widely preferred because of its increased solubility in water, in NPK solutions, and in ammoniated chelated micronutrient solutions.
However, a need still exists for a boron fertilizer which is even more soluble in water, in NPK solutions, and in ammoniated chelated micronutrient solutions.
Anger, Belgian Pat. No. 842,649, which is incorporated by reference, discloses a new class of water-soluble polyborates formed by the reaction of boric acid with an alkanolamine or an aliphatic polyamine. The preferred alkanolamines are monoethanolamine and aminoisopropanol. The preferred aliphatic polyamine is triethylene-tetraamine. Anger notes that such aqueous polyborate solutions can be used as thread impregnation agents, as refrigeration agents, as liquid purification agents, and as disinfection agents. There is no suggestion that any of these solutions might have an agricultural use as a boron fertilizer.